U.S. patent application number 14/770400 was filed with the patent office on 2016-01-07 for controlling a propellant distribution in a spacecraft propellant tank.
This patent application is currently assigned to AIRBUS DEFENCE AND SPACE LIMITED. The applicant listed for this patent is AIRBUS DEFENCE AND SPACE LIMITED. Invention is credited to Benjamin John Sapwell Nye.
Application Number | 20160001897 14/770400 |
Document ID | / |
Family ID | 47844228 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160001897 |
Kind Code |
A1 |
Nye; Benjamin John Sapwell |
January 7, 2016 |
CONTROLLING A PROPELLANT DISTRIBUTION IN A SPACECRAFT PROPELLANT
TANK
Abstract
A system for controlling a distribution of propellant in a
propellant tank assembly for a spacecraft comprises a body for
containing the propellant, a plurality of thermal tomography
elements, including a plurality of temperature-control elements and
a plurality of temperature sensors, disposed around the body for
detecting the distribution of the propellant inside the body; and a
tomography element control module arranged to control the plurality
of temperature-control elements to redistribute the propellant
inside the propellant tank body by heating and/or cooling the
propellant. In an embodiment, the propellant tank body includes a
propellant management device inside the body and the tomography
elements are disposed in proximity to the propellant management
device. Tomography data can be obtained from the plurality of
tomography elements, and a distribution of propellant within the
propellant tank body can be determined based on the obtained
tomography data.
Inventors: |
Nye; Benjamin John Sapwell;
(Stevenage, Hertfordshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AIRBUS DEFENCE AND SPACE LIMITED |
Stevenage, Hertfordshire |
|
GB |
|
|
Assignee: |
AIRBUS DEFENCE AND SPACE
LIMITED
Stevenage, Hertfordshire
GB
|
Family ID: |
47844228 |
Appl. No.: |
14/770400 |
Filed: |
February 26, 2014 |
PCT Filed: |
February 26, 2014 |
PCT NO: |
PCT/EP2014/053745 |
371 Date: |
August 25, 2015 |
Current U.S.
Class: |
60/204 ;
60/260 |
Current CPC
Class: |
B64G 1/402 20130101;
F05D 2270/303 20130101; G01F 23/288 20130101; F02K 9/605
20130101 |
International
Class: |
B64G 1/40 20060101
B64G001/40; F02K 9/60 20060101 F02K009/60 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2013 |
EP |
13275043.1 |
Claims
1. A system for controlling a distribution of propellant in a
propellant tank assembly for a spacecraft, the system comprising: a
body for containing the propellant; a plurality of thermal
tomography elements, including a plurality of temperature-control
elements and a plurality of temperature sensors, disposed around
the body for detecting the distribution of the propellant inside
the body; and a tomography element control module arranged to
control the plurality of temperature-control elements to
redistribute the propellant inside the propellant tank body by
heating and/or cooling the propellant.
2. The system of claim 1, further comprising: a propellant outlet;
and a propellant management device inside the body, arranged to
supply the propellant to the propellant outlet.
3. The system of claim 2, wherein the plurality of temperature
sensors are disposed in proximity to the propellant management
device.
4. The system of claim 2, wherein the plurality of
temperature-control elements include a plurality of coolers
disposed in proximity to the propellant management device.
5. The system of claim 2, wherein the plurality of
temperature-control elements include a plurality of heaters
disposed away from the propellant management device.
6. The system of claim 2, wherein the propellant management device
comprises one or more vanes.
7. The system of claim 1, wherein the plurality of thermal
tomography elements are disposed on an exterior surface of the
body.
8. The system of claim 1, wherein the tomography element control
module is further arranged to control the plurality of thermal
tomography elements to obtain tomography data, and the system
further comprises: a tomography data analysis module arranged to
receive the obtained tomography data and to determine a
distribution of the propellant inside the propellant tank based on
the obtained tomography data.
9. The system of claim 8, wherein the propellant tank assembly, the
tomography element control module and the tomography data analysis
module are included onboard the same spacecraft.
10. The system of claim 8, wherein the propellant tank assembly and
the tomography element control module are included onboard the same
spacecraft, and the tomography data analysis module is a
ground-based module arranged to receive the obtained tomography
data from the spacecraft.
11. A method of controlling the distribution of propellant in a
propellant tank assembly for a spacecraft, the propellant tank
assembly comprising a body for containing the propellant and a
plurality of thermal tomography elements, including a plurality of
temperature-control elements and a plurality of temperature
sensors, disposed around the body for detecting the distribution of
the propellant inside the body, the method comprising: controlling
the plurality of temperature-control elements to redistribute the
propellant inside the propellant tank body by heating and/or
cooling the propellant.
12. The method of claim 11, wherein prior to controlling the
plurality of temperature-control elements to redistribute the
propellant, the method further comprises: obtaining tomography data
from the plurality of thermal tomography elements; and determining
a distribution of propellant inside the propellant tank based on
the obtained tomography data.
13. The method of claim 12, further comprising: determining an
amount of the propellant remaining in the propellant tank based on
the determined distribution and a known density of the
propellant.
14. The method of claim 11, wherein controlling the plurality of
temperature-control elements to redistribute the propellant
comprises: comparing the determined distribution to a desired
distribution of propellant to identify one or more first regions
within the propellant tank body having a higher concentration of
propellant in the determined distribution than in the desired
distribution; and controlling the plurality of temperature-control
elements to heat the identified one or more first regions, and/or
wherein controlling the plurality of temperature-control elements
to redistribute the propellant comprises: comparing the determined
distribution to the desired distribution of propellant to identify
one or more second regions within the propellant tank body having a
lower concentration of propellant in the determined distribution
than in the desired distribution; and controlling the plurality of
temperature-control elements to cool the identified one or more
second regions.
15. The method of claim 11, further comprising: obtaining updated
tomography data from the plurality of thermal tomography elements,
after controlling the plurality of temperature-control elements to
redistribute the propellant inside the propellant tank body; and
determining an updated distribution of the propellant inside the
propellant tank based on the obtained tomography data.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to controlling a propellant
distribution in a spacecraft propellant tank. In particular, the
present invention relates to controlling a distribution of
propellant inside a propellant tank body using a plurality of
thermal tomography elements disposed around the body.
BACKGROUND OF THE INVENTION
[0002] It is a recurring requirement for space missions to provide
means by which propellant levels can be gauged and controlled
throughout the operational lifetime of a spacecraft. Conventional
methods for propellant gauging include a dead reckoning method, and
a thermal propellant gauging technique (TPGT). In the dead
reckoning method, the current propellant level is estimated by
subtracting an estimated mass of propellant burnt during all
thruster firings since the mission began, from the initial level of
propellant. This method and becomes increasingly inaccurate towards
the end-of-life due to accumulated errors. In the TPGT method, the
thermal response of the propellant tank to heating is measured and
compared to simulation results for different propellant levels. A
combination of dead reckoning and TPGT can also be used to estimate
the remaining propellant level. However, these methods do not
always satisfy the requirement for gauging accuracy throughout the
on-orbit lifetime, which is typically .+-.10% of remaining
propellant.
[0003] The invention is made in this context.
SUMMARY OF THE INVENTION
[0004] According to the present invention there is provided a
system for controlling a distribution of propellant in a propellant
Lank assembly for a spacecraft, the system comprising: a body for
containing the propellant; a plurality of thermal tomography
elements, including a plurality of temperature-control elements and
a plurality of temperature sensors, disposed around the body for
detecting the distribution of the propellant inside the body; and a
tomography element control module arranged to control We plurality
of temperature-control elements to redistribute the propellant
inside the propellant tank body by heating and/or cooling the
propellant.
[0005] The system can further comprise: a propellant outlet; and a
propellant management device inside the body, arranged to supply
the propellant to the propellant outlet.
[0006] The plurality of temperature sensors can be disposed in
proximity to the propellant management device.
[0007] The plurality of temperature-control elements can include a
plurality of coolers disposed in proximity to the propellant
management device.
[0008] The plurality of temperature-control elements can include a
plurality of heaters disposed away from the propellant management
device.
[0009] The propellant management device can comprise one or more
vanes.
[0010] The plurality of thermal tomography elements can be disposed
on an exterior surface of the body.
[0011] The tomography element control module can be further
arranged to control the plurality of thermal tomography elements to
obtain tomography data, and the system can further comprise: a
tomography data analysis module arranged to receive the obtained
tomography data and to determine a distribution of the propellant
inside the propellant tank based on the obtained tomography
data.
[0012] In an embodiment, the propellant tank assembly, the
tomography element control module and the tomography data analysis
module are included onboard the same spacecraft.
[0013] In another embodiment, the propellant tank assembly and the
tomography element control module are included onboard the same
spacecraft, and the tomography data analysis module is a
ground-based module arranged to receive the obtained tomography
data from the spacecraft.
[0014] According to the present invention, there is also provided a
method of controlling the distribution of propellant in a
propellant tank assembly for a spacecraft, the propellant tank
assembly comprising a body for containing the propellant and a
plurality of thermal tomography elements, including a plurality of
temperature-control elements and a plurality of temperature
sensors, disposed around the body for detecting the distribution of
the propellant inside the body, the method comprising: controlling
the plurality of temperature-control elements to redistribute the
propellant inside the propellant tank body by heating and/or
cooling the propellant.
[0015] Prior to controlling the plurality of temperature-control
elements to redistribute the propellant, the method can further
comprise: obtaining tomography data from the plurality of thermal
tomography elements; and determining a distribution of propellant
inside the propellant tank based on the obtained tomography
data.
[0016] The method can further comprise: determining an amount of
the propellant remaining in the propellant tank based on the
determined distribution and a known density of the propellant.
[0017] Controlling the plurality of temperature-control elements to
redistribute the propellant can comprise: comparing the determined
distribution to a desired distribution of propellant to identify
one or more first regions within the propellant tank body having a
higher concentration of propellant in the determined distribution
than in the desired no distribution; and controlling the plurality
of temperature-control elements to heat the identified one or more
first regions, and/or wherein controlling the plurality of
temperature-control elements to redistribute the propellant
comprises: comparing the determined distribution to the desired
distribution of propellant to identify one or more second regions
within the propellant tank body having a lower concentration of
propellant in the determined distribution than in the desired
distribution; and controlling the plurality of temperature-control
elements to cool the identified one or more second regions.
[0018] The method can further comprise: obtaining updated
tomography data from the plurality of thermal tomography elements,
after controlling the plurality of temperature-control elements to
redistribute the propellant inside the propellant tank body; and
determining an updated distribution of the propellant inside the
propellant tank based on the obtained tomography data.
[0019] The determined updated distribution of the propellant can be
compared to the desired distribution to determine whether the
desired distribution has been achieved.
[0020] According to the present invention, there is also provided a
spacecraft including the propellant tank assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Embodiments of the present invention will now be described,
by way of example only, with reference to the accompanying
drawings, in which:
[0022] FIG. 1 illustrates a propellant tank assembly according to
an embodiment of the present invention;
[0023] FIG. 2 illustrates a possible distribution of propellant in
the lower compartment of the propellant tank assembly of FIG. 1,
according to an embodiment of the present invention;
[0024] FIG. 3 illustrates an array of tomography elements disposed
around the body of a propellant tank, according to an embodiment of
the present invention;
[0025] FIG. 4 illustrates the collection of tomography data from an
array of tomography elements disposed around the body of a
propellant tank, according to an embodiment of the present
invention;
[0026] FIG. 5 illustrates an array of thermal tomography elements
disposed around the body no of a propellant tank, according to an
embodiment of the present invention;
[0027] FIG. 6 is a flowchart showing a method of determining an
amount of propellant remaining in a propellant tank, according to
an embodiment of the present invention;
[0028] FIG. 7 is a flowchart showing a method of using thermal
tomography elements to control propellant distribution in a
propellant tank, according to an embodiment of the present
invention;
[0029] FIG. 8 illustrates a system for determining a propellant
distribution in a propellant tank assembly, according to an
embodiment of the present invention; and
[0030] FIG. 9 illustrates a system for determining a propellant
distribution in a propellant tank assembly, according to an
embodiment of the present invention.
DETAILED DESCRIPTION
[0031] Referring now to FIG. 1, a propellant tank assembly
according to an embodiment of the present invention is illustrated.
The propellant tank assembly 100 comprises a body 101, which is a
hollow container for containing propellant. The propellant tank
assembly further comprises a membrane 102 disposed inside the body
101 to divide the body 101 into an upper compartment 103 and a
lower compartment 104, and a communication tube 105 around the
perimeter of the membrane 102. The communication tube 105 includes
a first opening 106 into the upper compartment 103 and a second
opening 107 into the lower compartment 104. The communication tube
105 allows communication of a fluid between the upper compartment
103 and the lower compartment 104.
[0032] The propellant tank assembly 100 further comprises a gas
inlet 108 in fluid communication with the upper compartment 103,
and a propellant outlet 109 in fluid communication with the lower
compartment 104. The reservoir of pressure within the body 101
provides the driving force to expel propellant from the propellant
outlet 109 whenever it is demanded by the downstream propulsion
system.
[0033] In addition, as shown in FIG. 1 the propellant tank assembly
100 can further comprise one or more propellant management devices
(PMDs) inside the body 101. In the present embodiment, the
propellant tank assembly 100 includes a control PMD 110, which is a
high-surface area structure in fluid communication with the
propellant outlet 109, and further includes a communication PMD in
the form of four vanes disposed on an interior surface of the body
101. In the present embodiment the four vanes are arranged at
angles of 0, 90, 180 and 270 degrees around the central axis of the
propellant tank 100, although only three of these vanes 111, 112,
113 are visible in the cut-away drawing illustrated in FIG. 1. The
communication PMD 111, 112, 113 and control PMD no are arranged to
draw propellant towards the propellant outlet 109 by capillary
action, to provide gas-free propellant to the propellant outlet
109.
[0034] Although in the present embodiment a communication PMD
including four vanes is provided, in other embodiments any number
of vanes may be used, that is, one or more vanes. Furthermore,
communication PMDs are not limited to vanes, and in other
embodiments a different communication PMD can be provided instead
of, or in addition to, one or more vanes. For example, instead of
vanes a communication PMD can comprise one or more galleries each
providing a covered flow path to the propellant outlet.
[0035] It will be understood that the propellant tank assembly 100
may be used in a microgravity environment, and that the terns
`upper` and `lower` here merely refer to the propellant tank in the
orientation shown in FIG. 1 and do not imply a particular
orientation of the propellant tank assembly 100 during use.
[0036] Referring now to FIG. 2, a possible distribution of
propellant in the lower compartment of the propellant tank assembly
of FIG. 1 is illustrated, according to an embodiment of the present
invention. As shown in FIG. 2, the propellant tank assembly 100
further comprises an array of thermal tomography elements 201
disposed around the body 101, which can be used to determine the
distribution of propellant 202 in the propellant tank. In the
example of FIG. 2, the liquid propellant 202 is situated toward the
sides of the lower compartment, and surrounds a bubble of
pressurant gas 203. This is a propellant distribution that would be
expected in a microgravity environment, in which the distribution
of liquid is largely governed by surface tension forces. As the
propellant 202 is consumed by the spacecraft, the volume of
propellant 202 remaining in the propellant tank assembly 100 will
decrease and the volume of the pressurant gas bubble 203 will
increase.
[0037] The thermal tomography elements 201 can be used to collect
tomography data which can be analysed to determine the distribution
of propellant 202 within the propellant tank assembly 100. The
thermal tomography elements 201 include a plurality of emitters and
a plurality of receivers, which enable the internal distribution of
liquid to be determined from the variation in attenuation
experienced by waves travelling along different paths through the
propellant tank body 101, between different emitters and
receivers.
[0038] By enabling the distribution of propellant in the propellant
tank 100 to be determined, embodiments of the present invention can
provide an improved method of determining the remaining propellant
levels. Being able to accurately determine the amount of propellant
remaining can enable the mission duration to be extended.
[0039] In the present embodiment a thermal tomography method is
used, and the plurality of tomography elements 201 include a
plurality of heaters and a plurality of temperature sensors. The
heaters can, for example, be resistive heating elements or peltier
heaters. The temperature sensors can, for example, be thermistors
or thermocouples. Other types of heaters and temperature sensors
could be used.
[0040] An additional benefit of using thermal tomography is that
the heaters in the array of tomography elements can be controlled
to apply thermal gradients to influence the distribution of
propellant within a tank, for example to move propellant towards
collection features in the propellant tank body 101 such as the
control PMD 110 and guide vanes 111, 112, 113. Controlling the
propellant in this way can increase the amount of propellant that
is recovered from the tank for end-of-life operation.
[0041] In the present embodiment the thermal tomography elements
201 are arranged in a regular array of strips, only one of which is
visible in FIG. 2. Each strip 201 includes a plurality of elements
attached to an exterior surface of the body. However, the invention
is not limited to a tomography array in which the elements are
arranged in strips. In general any geometry can be used for the
array of thermal tomography elements, for example in any direction
the elements may be regularly or irregularly spaced. Also, in other
embodiments the plurality of thermal tomography elements could be
disposed around the body 101 on an interior surface of the body
101, or in cavities within the wall of the body 101. When the
thermal tomography elements are disposed on an interior surface of
the body 101, the elements can be in direct fluid contact with the
propellant, enabling the use of techniques such as electrical
resistance tomography. In such embodiments, the thermal tomography
elements should be formed from materials which are chemically
compatible with the propellant.
[0042] Referring now to FIG. 3, an array of thermal tomography
elements disposed around the body of a propellant tank is
illustrated, according to an embodiment of the present invention.
FIG. 3 shows a cross-section through a propellant tank assembly 300
comprising a body 301 and four guide vanes 311, 312, 313, 314
inside the body 301. The thermal tomography elements 302, 303 are
disposed on an exterior surface of the body 301 in proximity to
each of the guide vanes 311, 312, 313, 314. In the present
embodiment the thermal tomography elements are arranged in strips,
similar to the embodiment of FIGS. 1 and 2, with two strips of
sensors 302, 303 disposed in proximity to each guide vane 311.
[0043] When a propellant tank assembly includes one or more PMDs,
for example guide vanes as shown in FIG. 3, the propellant
distribution will be concentrated around the guide vanes,
particularly when the tank is approaching depletion. Providing
thermal tomography elements which are disposed in proximity to the
PMDs has the advantage that the resolution obtainable by the
tomography array is enhanced in critical areas, where the greatest
variation in propellant surface profile exists.
[0044] Referring now to FIG. 4, the collection of tomography data
from an array of thermal tomography elements disposed around the
body of a propellant tank is illustrated, according to an
embodiment of the present invention. The left-hand diagram in FIG.
4 illustrates a vertical cross-section through the propellant tank
assembly 400 and the right-hand diagram illustrates a horizontal
cross-section through the propellant tank assembly 400, when the
propellant tank assembly 400 is in an upright position.
[0045] As shown in FIG. 4, the propellant tank assembly 400 of the
present embodiment comprises an array of thermal tomography
elements arranged in six vertical strips 402, 403 around the
propellant tank body 401, each strip including five tomography
elements. These numbers are merely exemplary, and in other
embodiments different numbers of thermal tomography elements may be
used and/or a different geometry can be used for the tomography
array. Each thermal tomography element can be either an emitter or
a receiver, or can be both an emitter and receiver.
[0046] In the example shown in FIG. 4, an emitter in one strip 402
of thermal tomography elements emits a thermal signal by local
heating or cooling, which is detected by receivers in another strip
403. This enables the attenuation of the thermal signal to be
determined along different paths through the body 401. The
tomography array of no emitters and receivers can measure the
attenuation of the thermal signal between different points around
the body 401 of the propellant tank assembly 400, and the
attenuation depends upon the composition through which it passes.
The tomography array can be used to obtain tomography data which
includes information about the attenuation between different points
around the body 401. A tomography algorithm can be used to
reconstruct a 3-dimensional map of the propellant tank contents
from the obtained tomography data.
[0047] By enabling the distribution of propellant within the
propellant tank assembly to be determined, embodiments of the
present invention offer several advantages over conventional
propellant gauging methods. For example, the mass of propellant
remaining in the propellant tank body can be determined by
calculating the volume of propellant from the obtained
3-dimensional map of the propellant tank contents, and multiplying
the volume of propellant by a known density of the propellant. This
can provide a more accurate measure of the mass of propellant than
conventional methods.
[0048] Another advantage of detecting the distribution of
propellant can be validation of a propellant tank design, by
confirming that the propellant is distributed in the intended
locations within the propellant tank body. Also, embodiments of the
present invention can provide visualisation of static residuals
towards the end-of-life, which is propellant that cannot be removed
from the tank surfaces.
[0049] Yet another advantage offered by embodiments of the present
invention is the ability to provide real-time monitoring of the
propellant distribution (hiring spacecraft manoeuvres. In
particular, for long-duration spacecraft manoeuvres the propellant
management devices (PMDs) within the propellant tank body may
become depleted or unwetted. When conventional propellant gauging
methods are used, it is normal practice to enforce a significant
safety margin on manoeuvre duration to allow for uncertainties in
propellant distribution. However, by using tomography to detect the
propellant distribution, embodiments of the present invention can
provide real-time confirmation that the PMDs remain wetted. This
can allow extended manoeuvre durations without having to
incorporate such large safety margins, thereby saving time in
spacecraft operation schedules.
[0050] Referring now to FIG. 5, an array of thermal tomography
elements disposed around a no propellant tank body is illustrated,
according to an embodiment of the present invention. Like FIG. 3,
FIG. 5 shows a cross-section through a propellant tank assembly 500
comprising a body 501 and four guide vanes 511, 512, 513, 514
inside the body 501. The thermal tomography elements 502, 503 are
disposed on an exterior surface of the body 501 in proximity to
each of the guide vanes 511, 512, 513, 514. In the present
embodiment the thermal tomography elements 502, 503 are arranged in
strips, similar to the embodiment of FIGS. 1 to 4, with two strips
disposed in proximity to each of the guide vanes 511, 512, 513,
514.
[0051] The thermal tomography elements include a plurality of
coolers 502 disposed in proximity to the PMDs 511, 512, 513, 514,
which in the present embodiment are guide vanes. The thermal
tomography elements also include a plurality of heaters 503
disposed around the body 501 at locations remote from the PMDs 511,
512, 513, 514. That is, the plurality of coolers 502 are located
closer to the PMDs than the plurality of heaters 503. The plurality
of coolers could be peltier-driven coolers. The heaters and coolers
can both be referred to as temperature-control elements.
[0052] In the present embodiment, the plurality of thermal
tomography elements 502, 503 can be controlled to redistribute
propellant to a desired distribution in which propellant is
concentrated at the PMDs 511, 512, 513, 514. Specifically, the
plurality of thermal tomography elements 502, 503 can be controlled
by cooling the coolers 502 located near to the PMDs 511, 512, 513,
514 while heating the heaters 503 located further from the PMDs
511, 512, 513, 514. This lowers the temperature of the PMDs
relative to other regions in the propellant tank assembly 500,
causing any remaining propellant to condense onto the PMDs 511,
512, 513, 514 and increasing the amount of propellant which can be
extracted as the tank becomes empty.
[0053] In other embodiments a plurality of thermal tomography
elements may only include a plurality of heaters or may only
include a plurality of coolers. In such embodiments the tomography
elements can still be arranged so that a plurality of first thermal
tomography elements 502 are disposed in proximity to one or more
PMDs and a plurality of second thermal tomography elements 503 are
disposed at locations remote from the PMDs, similar to the
arrangement shown in FIG. 5. That is, the first thermal tomography
elements 502 can be located closer to the PMDs than the second
thermal tomography elements 503. When both the first and second
thermal tomography elements 502, 503 are heaters, the thermal
tomography elements can be controlled to redistribute the
propellant to be closer to the PMDs by only heating the second
tomography elements 503, or by heating the second tomography
elements 503 to a higher temperature than the first tomography
elements 502. On the other hand, when both the first and second
thermal tomography elements 502, 503 are coolers, the thermal
tomography elements can be controlled to redistribute the
propellant to be closer to the PMDs by only cooling the first
tomography elements 502, or by cooling the first tomography
elements 502 to a lower temperature than the second tomography
elements 503. Both of these control methods can generate thermal
gradients within the propellant tank assembly 500 which will cause
propellant to condense onto the PMDs, by lowering the temperature
near the PMDs relative to other regions in the propellant tank
assembly too.
[0054] FIG. 6 is a flowchart showing a method of determining an
amount of propellant remaining in a propellant tank, according to
an embodiment of the present invention. In the first step S601,
tomography data is obtained from a plurality of thermal tomography
elements disposed on an exterior surface of a body of a spacecraft
propellant tank, for example a propellant tank assembly as shown in
any of FIGS. 1 to 5.
[0055] Then, in step S602, the distribution of propellant inside
the propellant tank is determined based on the obtained tomography
data. Here, the step S602 of determining the propellant
distribution can be carried out by processing the tomography data
onboard the spacecraft using a tomography algorithm. Alternatively,
the raw tomography data can be transmitted from the spacecraft to
another apparatus, for example a ground-based tomography data
analysis module, for processing.
[0056] Once the propellant distribution has been determined, the
amount of propellant remaining can optionally be determined in step
S603 based on the determined distribution and a known density of
the propellant. Specifically, the volume of propellant can be
calculated from the determined distribution and this can be
multiplied by the propellant density to give the mass of remaining
propellant.
[0057] FIG. 7 is a flowchart showing a method of using thermal
tomography elements to redistribute propellant in a propellant tank
body, according to an embodiment of the present invention. The
method can be implemented using any propellant tank assembly which
includes a plurality of thermal tomography elements. The method
takes advantage of a plurality of heaters and/or a plurality of
coolers included in the thermal tomography elements as emitters, by
using the heaters to locally heat regions of the propellant tank
assembly and/or by using the coolers to locally cool regions of the
propellant tank assembly, in order to redistribute propellant.
[0058] First, in step S701, tomography data is obtained from the
plurality of thermal tomography elements, and in step S702 the
distribution of propellant inside the propellant tank is determined
based on the obtained tomography data. These steps can be similar
to steps S601 and S602 in FIG. 6. Then, in step S703, the heaters
and/or coolers are controlled to redistribute the propellant inside
the propellant tank body by heating and/or cooling the
propellant.
[0059] To control thee heaters and/or coolers to redistribute the
propellant, various approaches are possible, as described above
with reference to FIG. 5. In the present embodiment, a plurality of
heaters are controlled by comparing the distribution determined in
step S702 to a desired distribution of propellant, to identify one
or more first regions within the propellant tank body having a
higher concentration of propellant in the determined distribution
than in the desired distribution. Then the plurality of heaters are
controlled to heat We identified one or more first regions, by
activating the heaters located closest to the identified one or
more first regions. Instead of, or as well as, controlling a
plurality of heaters, a plurality of coolers can be controlled by
comparing the distribution determined in step S702 to the desired
distribution of propellant, to identify one or more second regions
within the propellant tank body having a lower concentration of
propellant in the determined distribution than in the desired
distribution. Then the plurality of coolers are controlled to cool
the identified one or more second regions, by activating the
coolers located closest to the identified one or more second
regions.
[0060] In other embodiments alternative control methods could be
used. For example, a plurality of predetermined heater and/or
cooler control schemes could be stored, each corresponding to one
of a plurality of different predetermined distributions. One of the
plurality of predetermined distributions closest to the actual
distribution, as determined in step S702, can be selected, and the
predetermined heater and/or cooler control scheme associated with
the selected predetermined distribution can be used to control the
heaters and/or coolers. The predetermined heater and/or cooler
control scheme can, for example, identify which ones of the heaters
and/or coolers are to be switched on, and to what temperature each
heater or cooler should be set.
[0061] After controlling the heaters and/or coolers, updated
tomography data is obtained in step S704 and an updated propellant
distribution is determined in step S705. These steps can be similar
to steps S701 and S702. Next, in step S706 the updated propellant
distribution is compared to the desired distribution. If the
updated propellant distribution matches the desired distribution,
either exactly or within a predetermined acceptable margin of
error, the method ends. On the other hand, if it is determined that
the desired distribution has not been achieved, the method returns
to step S703 and selectively controls the heaters again to
redistribute the propellant further.
[0062] Here, the desired distribution can be a distribution in
which the propellant is distribution in the intended locations, for
example on and around any PMDs included inside the propellant tank
body. Also, although in the present embodiment it is checked
whether the desired distribution has been achieved, in other
embodiments it could be assumed that the selective heating of the
propellant tank has had the desired effect, and steps S704 to S706
could be omitted.
[0063] Referring now to FIG. 8, a system for determining a
propellant distribution in a propellant tank assembly is
illustrated, according to an embodiment of the present invention.
The system comprises a propellant tank assembly including a
plurality of thermal tomography elements 801, for example a
propellant tank assembly as shown in any one of FIGS. 1 to 5. The
system further comprises a tomography element control module 802
arranged to control the plurality of thermal tomography elements
801 to obtain tomography data, and a tomography data analysis
module 803 arranged to receive the obtained tomography data and to
determine a distribution of the propellant inside the propellant
tank based on the obtained tomography data. The propellant tank
assembly including the thermal tomography elements 801, the
tomography element control module 802 and the tomography data
analysis module 803 are included onboard the same spacecraft 800.
This arrangement may be preferred when, for example, the spacecraft
is a manned spacecraft and We crew require access to the processed
tomography data, i.e. the determined 3-dimensional map showing
propellant distribution within the propellant tank.
[0064] Referring now to FIG. g, a system for determining a
propellant distribution in a propellant tank assembly is
illustrated, according to an embodiment of the present invention.
The system is similar to that of FIG. 8, except that in the present
embodiment the propellant tank assembly including the thermal
tomography elements 901, and the tomography element control module
902, are included onboard a spacecraft 900, whilst the tomography
data analysis module 903 is a ground-based module arranged to
receive the obtained tomography data from the spacecraft 900.
[0065] In the systems of both FIGS. 8 and 9, the tomography element
control module 802, 902 can be further arranged to control the
plurality of heaters and/or coolers to redistribute the propellant
inside the propellant tank body by heating the propellant, using
methods such as the ones described above with reference to FIGS. 5
and 7.
[0066] It will be understood that the present invention can be
applied to any type of propellant tank assembly, and embodiments of
the present invention are not limited to the propellant tank design
shown in FIGS. 1 to 5.
[0067] Whilst certain embodiments of the present invention have
been described above, it will be understood that many variations
and modifications are possible without departing from the scope of
the invention as defined in the claims.
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